1. Field of the Invention
The present invention relates generally to the formation of a metal onto a polyimide film and more particularly to the formation of multi-element, thin, hot film sensors on a polyimide film.
2. Description of the Related Art
The formation of a metal onto a polyimide film has important applications in the formation of multi-element, thin, hot film sensors. Sensors of this type are used to investigate boundary layer behavior on an airfoil surface, in order to design airfoils having higher lift and lower drag. For example, U.S. Pat. No. 4,848,153 to Stack et al., discloses the use of a multi-element sensor located on an airfoil to simultaneously detect laminar flow separation and reattachment by sensing the phase reversal in specific regions. Measurements of boundary layers typically have been made using pressure tube and hot-wire probes, both of which intrude into the boundary-layer flow and exhibit relatively poor resolution.
Existing methods of thin-film metallization of polyimides or other polymer films include: vapor deposition, sputter deposition and adhesive bonding sheets of metal foil. However, current practice using these techniques generally results in poor adhesion between subsequently applied metal layers. In contrast, the present invention results in thin sensors with excellent adhesion between metal layers.
In the present invention, each sensor element is formed by simultaneously bombarding a non-conductive polyimide layer with an ion beam while electron beam evaporating a layer of nickel onto the polyimide surface. Copper-coated nickel film electrical leads are then connected to each sensor element.